1. Field of the Invention
The present invention relates to a technology for removing a foreign substance, such as dust, adhering to a surface of an optical member provided on an optical axis of an optical apparatus, such as an imaging apparatus.
2. Description of the Related Art
In imaging apparatuses, such as digital cameras, which perform imaging of a subject by converting a subject image into an electrical signal, an imaging light-beam is received by an image sensor. Then, a photoelectric conversion signal output from the image sensor is converted into image data. The image data is recorded on a recording medium, such as a memory card. A charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor can be used as the image sensor.
In such imaging apparatuses, an optical low-pass filter or an infrared cut filter is disposed on a subject side of the image sensor. When foreign substances, such as dust, adhere to the surfaces of the filter, the foreign substances produce black spots in a captured image. Consequently, visual quality of the image deteriorates.
In particular, in digital single-lens reflex cameras with interchangeable lenses, mechanical operating units, such as a shutter and a quick-return mirror, are disposed in the vicinity of an image sensor. Sometimes, foreign substances, such as dust, are generated by the operating units and adhere to the surface of the image sensor or the filter. In addition, when the lens is changed, a foreign substance, such as dust, may enter the camera body from an opening of a lens mount and may adhere to the surface of the image sensor or the filter.
In order to avoid such phenomena, U.S. Patent Application Publication No. 2004/0169761 A discusses a technology for providing a dust-proof film, which transmits an imaging light-beam, on an object side of an image sensor, and for vibrating the dust-proof film using a piezoelectric element to remove a foreign substance, such as dust, adhering to the surface of the dust-proof film.
More specifically, U.S. Patent Application Publication No. 2004/0169761 A discusses a camera in which a dust-proof optical member is disposed between an image sensor and a mechanical shutter and below a finder optical system. In addition, a vibrating member for vibrating a peripheral edge portion of the optical member is provided in the camera and causes the optical member to perform resonant vibrations while switching between first-order and second-order vibration modes each having point-symmetric nodes. Consequently, dust adhering to the surface of the optical member can be removed.
In the camera discussed in U.S. Patent Application Publication No. 2004/0169761 A, when the optical member is caused to perform resonant vibrations, a supporting member is made to contact a portion corresponding to a node generated in the vicinity of a vibrating end of the optical member, at which a vibrating member is provided. However, in the case of using a plurality of vibration modes, it is unclear what vibration mode includes a node corresponding to the portion which the supporting member is made to contact. Considering a configuration in which the vibrating member is provided at one of opposite sides of the rectangular optical member, the optical member has a vibrating end (side at which the vibrating member is provided) and a free end (side at which the vibrating member is not provided) opposite the vibrating end. Generally, in a case where the supporting member is made to contact a portion other than those corresponding to nodes of a vibration, the vibration is attenuated. However, a degree of attenuation of the vibration in the vicinity of the free end is significantly high, as compared with that of attenuation of the vibration in the vicinity of the vibrating end. When the vibration of the optical member is largely attenuated, it is difficult to remove dust adhering to the surface of the optical member. Therefore, when the supporting member is made to contact a portion corresponding to a node of the vibration in the vicinity of the free end in the configuration in which the vibrating member is provided at one of opposite sides of the rectangular optical member, it is very important what vibration mode is selected in which a node corresponding to a portion contacting the supporting member is generated in the case of using a plurality of vibration modes.
In addition, when the supporting member is made to contact a portion corresponding to a node in a certain vibration mode in the case of using a plurality of vibration modes, an amplitude in that vibration mode may be too large. Accordingly, there is a fear of breakage of the optical member.